A train making the first run along a faster route has hurtled off an overpass in the US and spilled some of its carriages on to the road below, killing at least six people, authorities said.
Seventy-eight passengers and five crew members were aboard when the Amtrak train travelling at more than 80mph derailed about 40 miles south of Seattle on a route that had raised safety concerns. T he death toll is expected to rise.
An official briefed on the investigation said preliminary signs indicated that Train 501 may have struck something before going off the track.
Pierce County Sheriff's Office said several vehicles on Interstate 5 were struck by falling train carriages and multiple motorists were injured. No motorists were reported killed.
Chris Karnes was on the train, three or four carriages from the front. He said the only part of the train remaining on the tracks was the rear locomotive. Several cars were hanging over the overpass.
The possibility that the wreck was caused by something on the tracks fed into concerns voiced by local officials about the risk of high-speed trains crossing busy streets. The mayor of a town near the derailment had warned about the danger of an accident at a public meeting two weeks ago.
Daniel Konzelman, 24, was driving parallel to the train on his way to work in Olympia. He was about 30 seconds ahead of the train on the freeway when he saw it derail.
Mr Konzelman, who was driving with a friend, said he pulled off the freeway and ran down along the tracks and over the bridge to get to the scene.
They saw three cars and a truck on the freeway that had been damaged by the derailment. There were train carriages with their roofs ripped off, or that were tipped upside down, on both sides of the track or turned sideways on the bridge.
They climbed into train carriages and found people hurt - some pinned underneath the train, others who appeared to be dead, he said. If they were mobile and seemed stable, he helped them climb out. If they appeared seriously hurt, he tried to comfort them by talking to them.
"I just wanted to help people because I would want people to help me," he said. "I'm an Eagle Scout. I have a lot of first-aid training and emergency response training."
"I prepared for the worst and hoped for the best. I saw a little bit of both," he said.
Donald Trump used the derailment to call for more infrastructure spending in a tweet sent about three hours after the accident.
He said the wreck, on a newly completed bypass, shows "more than ever why our soon to be submitted infrastructure plan must be approved quickly".
The train was making the inaugural run on the new route as part of a 180 million dollar (£134 million) project designed to speed up service by removing passenger trains from a route along Puget Sound which is bogged down by curves, single-track tunnels and freight traffic.
The new route includes a bypass built on an existing inland rail line that runs along Interstate 5 from Tacoma to DuPont, near where Train 501 derailed.
Track testing was completed in January and February, according to Washington State Department of Transportation.
The mayor of Lakewood, a city along the new route, predicted a deadly crash - but one involving a fast-moving train hitting a car or pedestrian at a crossing. At a recent public meeting, he called on state planners to build overpass-like rail structures instead of having trains cross busy streets.
"Come back when there is that accident and try to justify not putting in those safety enhancements," Don Anderson said, according to Seattle television station KOMO.
"Or you can go back now and advocate for the money to do it, because this project was never needed and endangers our citizens."
The National Transportation Safety Board said a team of investigators was on its way to the scene from Washington DC.
The train was going 81.1mph moments before the derailment, according to transitdocs.com, a website that maps Amtrak train locations and speeds using data from the railroad's train tracker app.
The maximum speed along the stretch of track, known as Point Defiance Bypass, is 79mph, according to information about the project posted online by Washington State Department of Transportation.
Hospital officials said of those injured at least two were in a critical condition and 11 others were seriously injured.
Four hospitals said 50 people were being treated for their injuries.
Authorities said a total of 13 train cars had derailed.
Washington State Patrol spokeswoman Brooke Bova said five vehicles and two semi-trailers underneath the train on I-5 were hit when the cars came off the tracks from above.